1. Field of the Invention
The present invention relates to an improvement in an automatic focusing device which is provided with driving means for driving a focusing lens, amount-of-driving detecting means for detecting the amount of driving of the focusing lens, and the like. The automatic focusing device may be disposed in an automatic focusing lens unit, or partly in the automatic focusing lens unit and partly in a camera (body).
2. Description of the Related Art
It has heretofore been common practice to manually bring a subject into focus during photography using a camera. In recent years, however, products such as autofocus cameras or autofocus lens units have become highly popular. In such products, an actuator, such as a DC motor or an ultrasonic motor, is provided in a camera (body) or a lens unit so that focusing can be automatically performed by directly moving a focusing lens. Accordingly, the accuracy of focusing is improved and the time required to achieve an in-focus state is greatly reduced, so that even a beginner can easily take a satisfactory photograph without missing a shutter opportunity.
However, the current autofocus cameras which have been improved in focusing speed over conventional manual-focus products have encountered the problem that an increased risk of abrasion of a moving part due to friction or the like occasionally leads to an impairment in mechanical durability. In the case of such an autofocus product, as the initial performance is gradually degraded, the probability that the focusing lens is driven over and over again during a focusing operation becomes higher. In the worst case, a hunting phenomenon may occur in focusing and it may become impossible to focus a subject.
In addition, if the autofocus product continues to be used for a long time, a mechanical looseness or the like increases in the focusing part of the lens unit, with the result that the reliability of focusing accuracy may become low.
In addition, if a user sends such a product to a manufacturer for repair, the components of the focusing part of the lens unit will have to be replaced and the user will have to pay a considerable repairing charge.